The study described in this proposal is designed to dissect the subcellular localization of presenilin 1 (PS1) by characterizing discrete targeting domains(s) within the protein. Mutations within PS1 cause familial, early-onset Alzheimer's disease (FAD) in affected families. PS1 is a ubiquitously expressed integral membrane protein, predominantly localized to the endoplasmic rteticulum. The subcellular distribution of N-terminal deletion mutants of PS1 will be further characterized. In addition, a small sequence currently thought to direct the ER localization of PS1 will be inserted into a normally cell surface protein, the vesicular stomatitis virus coat-glycoprotein (VSVG). The effect this presumptive PS1 targeting domain will have on the ER retention of VSVG chimeras will be characterized in detail. Finally, amino substitutions found within this domain in FAD families will be introduced and their impact on trafficking determined. It is anticipated that characterizing the ER targeting of PS1 will contribute to our understanding of the normal role for this protein, as well as to our understanding of the interplay between PS1 mutations and the ER processing of amyloid precursor protein that yields Abeta.